Exemplary embodiments of the invention relate to a belt tightener for tightening a safety belt in a vehicle. Exemplary embodiments also relate to a safety belt device comprising a belt tightener of this kind. Furthermore, exemplary embodiments relate to a method for operating a safety belt device of this kind.
A belt tightener is generally known as a passive safety device that is intended to be arranged in a vehicle. By means of a belt tightener of this kind, a safety belt can be automatically tightened in the case of a collision or an imminent collision of the vehicle such that the safety belt is tightened against the body of a vehicle occupant. As a result, the vehicle occupant participates in a total deceleration of the vehicle caused by the collision comparatively early. A reversible belt tightener comprises an electric motor and is coupled to a belt retraction device of a safety belt device. Alternatively or additionally, pyrotechnic belt tighteners are used, which are not reversible, however. The safety belt device is also coupled to a driver assist device for actuating the belt tightener, the driver assist device comprising sensors for detecting collision-related information.
Exemplary embodiments of the invention are directed to a belt tightener that is improved with respect to the prior art, an improved safety belt device comprising a belt tightener of this kind, and an improved method for operating a safety belt device of this kind.
According to embodiments of the invention, a belt tightener for tightening a safety belt in a vehicle comprises an impulse screw drive unit.
In the impulse screw drive unit, a force is transmitted from a drive component to an output component that can be connected to the belt retraction device, the drive component and the output component being mechanically decoupled from one another in the second ignition stage. In this case, force is not transmitted continuously, but in a pulse-like manner, with generated angular momentum peaks increasing asymptotically. The second ignition stage is activated, in particular, in the case of an impending unavoidable collision.
Even though the term “ignition stage” suggests pyrotechnics, here and in the following, this generally means an actuation stage occurring without the use of pyrotechnics, if not otherwise clear from the context.
By means of the impulse screw drive unit, a maximum torque of a belt retraction device that can be connected to the belt tightener can be increased with respect to conventional electromotive belt tighteners when the second ignition stage is activated. This makes it possible to generate a tightening force that is as comparably high as a tightening force that can be generated by means of a pyrotechnic belt tightener. The belt tightener is in this case reversible and can be reused after its actuation, i.e., after a collision. In particular, by means of the impulse screw drive unit, a number of electrical connection elements can be reduced with respect to conventional belt tighteners that comprise an additional pyrotechnic ignition unit. The pyrotechnic ignition unit in a conventional belt tightener having a second ignition stage requires its own cable set for the pyrotechnic tightener. A control device connected to the belt tightener likewise requires a second output for controlling the second ignition stage. By means of the impulse screw drive unit, the two ignition stages of the belt tightener can be activated using just one cable set and an overcurrent control means. The belt tightener therefore has a simple control system and is purely mechanical.
In other words: Nowadays, vehicles that have PRE-SAFE and reversible retraction tighteners experience reversible retraction tightening before the collision and in the case of a detected critical situation. The pyrotechnic retraction tightener is then ignited during the crash. Using the invention, the PRE-SAFE phase would remain the same and the electric motor would tighten the belt. Activating the second ignition stage or actuation stage before or during the crash is new. This sets the described impulse mechanism in the same unit into action.
According to one embodiment, the impulse screw drive unit comprises an electric motor as a drive component, a container filled with a hydraulic fluid and an output component, the electric motor being connected to the container for conjoint rotation and the output component being arranged at least in part in the container. As a result, when the second ignition stage is activated, hydraulic coupling between the electric motor and the output component is possible such that a higher torque can be transmitted to the output component than the electric motor can generate. When the first ignition stage is activated, the electric motor and the output component are mechanically coupled to one another, since a lower torque is sufficient in this case. The electric motor is therefore mechanically decoupled from the output component when the second ignition stage is activated. An impulse screw drive unit structure of this kind is already known. The impulse screw drive unit can thereby be simply integrated in the belt tightener.
Force is in this case transmitted from the electric motor to the output component via the hydraulic fluid in the container, the hydraulic fluid being an oil, for example, in particular a hydraulic oil. The container comprises a receiving region for receiving the hydraulic fluid, which region has an elliptical cross-section, for example. An inner diameter of the receiving region is in this case reduced by means of at least one rib-like projection which projects radially inwards. For example, four projections are provided which are equally distributed over a circumference of the receiving region. The shape of the cross-section and the reduced inner diameter in this case make it possible to seal particular regions of the receiving region such that the hydraulic fluid can dam up therein and exert pressure on the output component.
Alternatively, the impulse screw drive unit can also have a spring element instead of a hydraulic fluid, which spring element is coupled to the output component and the electric motor. The electric motor is in this case mechanically decoupled from the output component when the second ignition stage is activated. This makes it possible for pretensioning of the spring element to be influenced by means of the electric motor, with a pulse-like rotational movement of the output component occurring when the pretensioning is triggered.
The output component passes through the receiving region and is a spindle, for example, which has at least one drive element that projects radially outwards in the region of the container. In particular, the output component has two drive elements that are opposite one another in the circumferential direction. By means of the drive elements, the output component has a particular outer diameter corresponding to an inner diameter of the receiving region that is formed by means of two opposing rib-like projections. The drive elements are used in this case to transmit force from the hydraulic fluid to the output component or from the spring element to the output component.
The container is rotated about a rotational axis by means of the electric motor when the impulse screw drive unit is in operation. In this case, a rotational speed of the container is constant. Within the first ignition stage, the output component is rotated together with the container, since the electric motor is in this case still mechanically coupled directly to the output component. In the second ignition stage, the electric motor is decoupled from the output component such that the container and therefore also the receiving region comprising the projections, which region is filled with the hydraulic fluid, move relative to the output component. If the projections reach the same angular position as the drive elements during a rotation of the container, partial regions of the receiving region are sealed from one another since the drive elements abut the projections. This produces chambers that have different pressures since, as a result of the inertia, the hydraulic fluid flows further in the drive direction and a pressure is therefore exerted on the drive elements in the drive direction. The drive elements are therefore subjected to this pressure and convey the pressure to the output component to which the drive elements are rigidly connected. As a result, the output component rotates relative to the container until the drive elements do not abut the projections and the hydraulic fluid can flow freely again. This short rotational movement occurs in pulses. Since the output component can be rigidly connected to the shaft of the belt retraction device, this also rotates in pulses when connected.
After the pulse-like rotational movement of the output component, the container further rotates relative to the output component until the projections again reach the same angular position as the drive elements. This process repeats with each rotation of the container. As the number of rotations increases, the pulse-like rotational movements become asymptotically greater until a maximum value is reached. In so doing, a maximum torque of the output component can be increased with respect to a direct coupling to an electric motor. The maximum torque is in this case comparable to a maximum torque when a pyrotechnic belt tightener is used.
A safety belt device of a vehicle is also provided which comprises a belt retraction device comprising a shaft for unwinding and winding a safety belt in the vehicle and a belt tightener according to the invention or an embodiment of the belt tightener.
The safety belt device designed in this way makes it possible to use a reversible belt tightener that generates a tightening force when a second ignition stage is activated, which force is as comparably high as a tightening force that can be generated by means of a pyrotechnic belt tightener. As a result, the tightening force can be adapted, in particular, to an occupant and collision severity.
For this purpose, the output component of the impulse screw drive unit is connected to the shaft of the belt retraction device for conjoint rotation, such that a maximum torque can be transmitted to the shaft of the belt retraction device.
In a further embodiment, the safety belt device comprises a control unit coupled to the belt tightener, the control unit being coupled to a plurality of detection units for detecting collision-relevant information, and it being possible, by means of the control unit, to generate a control signal based on detected collision-relevant information in order to activate the belt tightener. The tightening force can therefore be adapted to an occupant and collision severity by means of the control unit. Furthermore, it is also possible, by means of the control unit, to activate the belt tightener even before the collision has occurred, such that the window of time until the maximum torque is reached is optimally used and the occupant participates in a total deceleration of the vehicle caused by the collision comparatively early. In this case, activation of the second ignition stage of the belt tightener is required, in particular, in the case of a collision that is classified as unavoidable.
A method for operating a safety belt device of a vehicle is also provided, in which the belt tightener is activated before the occurrence of a detected impending collision of the vehicle and a required tightening force is specified based on the collision-relevant information. In this case, a first ignition stage of the belt tightener is activated at a specific tightening force, at which the output component rotates so as to correspond with the electric motor. A second ignition stage of the belt tightener is activated at a further specific, in particular higher, tightening force, at which the output component rotates relative to the electric motor in a pulse-like manner. In this case, a period of time until the maximum torque is reached can be optimally used such that the occupant is positioned in the direction of a backrest comparatively early, as a result of which the danger of the cervical spine overstretching, which is referred to as the whiplash effect, is substantially avoided or at least reduced.
Parts which correspond to one another are provided with the same reference numerals in all drawings.